Bis-thioamide vulcanization accelerators



United States Patent BIS-THIOAMIDE VULCANIZATION ACCELERATORS HarrisWalton Bradley andPeter Kovacic, Wilmington,

Del., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del.,a corporation of Delaware N0 Drawing. Application May 18, 1954 SerialNo. 430,718

6 Claims. (Cl. 260-795) This invention relates to the vulcanization ofnatural and synthetic rubber and more particularly to the vulcanizationof polychloroprene using new and effective low temperature vulcanizationaccelerators.

Polychloroprene is a generic name applied to the polymers of2-chloro-1,3-butadiene (chloroprene), and to copolymers of the same withminor amounts of copolymerizable dienes or vinyl compounds such asacrylonitrile, butadiene, isoprene, dichlorobutadiene, and styrene.These polychloroprenes (which term is used to include copolymers) may bemade in aqueous emulsions and are available today under such names asneoprene type GN, neoprene type W, neoprene type PR, and as laticesunder type numbers such as type 571, type 735, and type 842, all ofwhich are generally referred to as polychloroprenes or chloroprenepolymers.

Although many compounds have been found to be very effective inaccelerating the vulcanization of natural and synthetic rubber by meansof sulfur and also for carrying out an analogous transformation ofneoprene to the elastic, non-plastic state, further improvement is stilldesirable. Thus it is desirable to find new accelerators which areeffective at lower vulcanization temperatures than are now practical butwhich, on the other hand, do not cause vulcanization at the temperaturesat which the rubber stocks are mixed, stored, and handled before thevulcanization step. In the case of polychloroprene, an additional reasonfor avoiding a premature reaction between the accelerator and theelastomer is that such reactions often generate hydrochloric acid whichcoagulates the latex before it can be used.

This invention has as an object to provide a class of compounds usefulas vulcanization accelerators. A further object is to providevulcanization accelerators for polychloroprene temperatures and whichshow little of the undesirable effects produced by most very activeaccelerators. A still further object is to provide vulcanizationaccelerators which are useful in the rapid curing at relatively lowtemperatures of articles made from polychloroprene latex. Other objectswill appear hereinafter. I

These objects are accomplished by the following invention ofincorporating into a vulcanizable polychloroprene from 0.2 to 5.0% byweight of a bisthioamide selected from the group consisting ofbisthioamides having the following formulae:

which are effective at low vulcanization K '5 ice wherein R is amonovalent hydrocarbon radical of from 1 to 20 carbon atoms, R is adivalent hydrocarbon radical of from 1 to 20 carbon atoms with bothvalences on the same carbon atom and R is a divalent hydrocarbon of from2 to 20 carbon atoms with the valences on different carbon atoms. Thehydrocarbon radicals of R, R and 11'' may be either saturated orunsaturated, aliphatic or aromatic and include the cycloalkyl andaralkyl radicals. These bisthioamides are very effective low temperaturevulcanization accelerators for neoprene and are particularly useful inthe rapid curing at relatively low temperature of articles made fromneoprene latex.

The range of most effective concentration of bisthioamide to beincorporated into the vulcanizable neoprene is from about 0.2 to 5.0% byweight and preferably from 0.5 to 2.0%. Any vulcanization temperaturemay be used; however, the lower. temperatures in the neighborhood of toC. are the most useful, since they permit good cures in short periodswhereas the usual accelerators give incomplete cures at thesetemperatures unless the curing time is much extended.

The'N,N-disubstituted dithioamides used in the present invention may bemade by the reaction of phosphorus pentasulfide with the correspondingdiamide or, more conveniently by the reaction of the appropriatedinitrile, amine, and hydrogen sulfide as fully described in U. S. P.2,201,170 and 2,280,578. Thus adiponitrile, butylamine, and hydrogensulfide give N,N-dibutyl dithioadipamide, as follows: NO-(CHzh-ON 2001mm211 s The following examples will better illustrate the nature of thepresent invention; however, it is to be understood that the invention isnot intended to be limited to these examples. The parts used are byweight unless otherwise specified.

In Examples 1 to 14, a latex, made by polymerizing chloroprene,containing 0.5% of sulfur, in an aqueous emulsion in which theemulsifying agent is the sodium salt of disproportionated rosin, wascompounded as follows:

Parts Polychloroprene latex solids 100 2,2'-methylene bis(6-tertiarybutyl-p-cresol) 1 Zinc oxide 5 Sulfur 2 Accelerator (as in tables) 2Each of the compounding ingredients used was added to the latex as adispersion in the conventional manner. The following formulation wasused in providing an aqueous dispersion of each accelerator:

Parts Ingredient to be added 8 Casein, 10% sol on 5 Sodiumdinaphthylmethane sulfonate 15 Water 22 n the tables.

prepared by the usual dipping termined, as shown in the tables.

For comparison, values obtained Without accelerator (control) and withdi polychloroprene accele ours, at 70 C., and further The cured filmsrious elongations, t break were dephenyl thiourea, a recommended rator,and in some cases, epsilon- Additional bisthioamides within the scope ofthe present invention which have been tested and which have given curessimilar to those 'of the above tables are:

(1) N,N'-dimethyl dithioadipamide (2) N,N'-diallyl dithioadipamide (3)N,N-dibenzyl dithioadipamide (4) N,N'dilauryl dithioadipamide (5)N,N'dibutyl dithio-suberic amide (6) N,N'-dimethyl octadecanedicarboxylic acid dithiothiocaprolactam, another excellent accelerator,are iiiamide eluded. In some cases, several values are given, to show 7-i h ihite htaicamide the range ordinarily obtained. The improvement obgg gz tained by the use of the present invention is particularly h 1 y pl noticeable in the modulus indicating a more complete (9) yene i e)(l0) N,N-ethylene b1s(thiooleam1de) cure' TABLE I (ll)N,N'-eicosarnethylene bis(thiobenzamide) (l2)3,6-distearyl-2,5-piperazine dithione M d 1 m (13)3,6-diphenyl-2,5-piperazine dithione D HUS ongal I 3 g gg g l" $50075 'gl i 5 5: To illustrate the stability of latices containing the pmm a o 6$5 (p s. i.) (De i Cent) accelerators of the present invention, a latexcompounded (D- with 2% of N,N-dibutyl dithioadipamide, as in Example 2,was stored for 20 days at room temperature. There 1 N,N-Di-n-propyl-60/100 525 2. 2 780 was no coagulation and the final pH was 11.6. On thed 6 12 ,3 0 1,975 5"0 2 a g 681108 1 520 2,850 other hand, the samelatex compounded with 2% of 3 gifg g gi fi ggflgg E3 3 23 25thiocaprolactani, as in one of the compositions used for Na3% l F 1,2503: 3 comparison in Table lihlwlashcoagulaied in thisttimelth f 4 Ii'CYCO 60100 400 final pH bein 10.4. e t iocapro actam is ypica o d'th'1- 1 60120 1,350 2,450 550 a 5 Nfl l' i piig y i e g 60100 350 2.600 020other rapid accelerators in rapidly generating acid in 6 gqfgig gggf28%}; 23 3 222 238 the presence of neoprene even at room temperature.The

""" Znthioh dmmiii 60/120 1.32 5 2425 580 compounds of the presentinvention do not do this teven cmeamidethough their vulcanizing actionat curing tempera ures N\I'-Di- -b t 1- 60100 575 2. 7'0 710 I'ilithioii dioihu- 60ii20 1,150 2,250 580 is believed to be due in partto reaction with the polyconami chloroprene.

N,N-Eth leno bis 60 200 425 2, 025 940 (thioben zamidc). 00/100 1, 2502,100 570 Although the bisth oamides of th s invention find their i gggfggflgg 322 $38 greatest use in the curing of films, thin-walledarticles, and s do 60/100 32 5 31115 360 other structures formed frompolychloroprene latex, thley 60120 600 ,200 650 {1 i to soid Control (noceleb 60/100 275 2,700 990 are also useful when incorporated d1 ec y neraitor). 0/150 1, 3 1 types of neoprene. 0 0 0 t 00/120 325 2, 600 950Example 15 Using a plastic type of solid elastomer made by poly- TABLE Hmerizing chloroprene in emulsion in the presence of a long-chainmercaptan, the following stock was made up Modulus rubber mill and wasthen cured Ex. Accelerator Com- Cure, at 600% Tensile tion At m theuspal i i No. pound (2%) Min./ Elonga- Strength Break for 0 111111- a 3o Q, tiorr) (p. s. i.) (percent) Parts Neoprene 100 9 l- N,N-Di-n-buty130 100 550 2, 075 000 Carbon black 30 dithifladipamideggfigg I2 238 $8228 Phenyl betanaphthylamme l J I Y 10 N.N-1l1)ipentg; 30 100 50 250Magfleslum OXlde 5 met lene 'tliio- 60 100 50 7 1.0 adipa inide. 00/1202,100 2, 575 620 oiude 3,6-Diisobuty1-2, 5- 30/100 775 2,575 000 N,N-dibutyl dithioadipamide 1 plixperaziue di- 00/100 1, 000 a, 250 000 tione. Epsilon thiocapro- 30/100 600 2, 650 900 An excellent f flobtained lactam. 60/100 850 2. 850 620 In the vulcanization process ofthe present invention 9 33333 5: S38 any type of the vulcanizablepolychloroprene stock known phenylthiourea 00/ 00 600 2,575 880 to theart may be used. These usually contain a poly- 6 120 ],'00 2,8" 690Control n acoeler- 3851 0 3 950 valent metal oxide, particularly zincoxide, magnesium atonggfigg 3 552 358 oxide and litharge and most oftena mixture of the first two. Sulfur is often used addition, but it shouldbe point- 1s1jght1y xtrapo1at d ed out that the compounds of the presentinvention are TABLE III Modulus Elonga- Amount, Cure, at 600% Tensiletion At No. Accelerator Compound percent Min./ C. Elonga- Strength Breaktion (p. s. 1.) (percent) p. s. i.

12 N,N'-Di-n-butyl dithio- 2 %8 Z28 di amide. a p I 60/100 850 2, 900800 8/ 8 03 2222 s33 6 i0 K' 60/120 800 3,300 880 adlpamlde- 60/100 4752, 750 980 Gontrolhio accelerator) 60/120 350 2,825 980 effective inboth the presence and absence of sulfur, their accelerating effect notbeing limited to the type of vulcanization which is caused by sulfur.

It is apparent from the preceding description that the bisthioamides ofthe present invention are efiective low temperature vulcanizationaccelerators in that they permit good cures in short cycles and at thesame time show little of the undesirable eifects produced by other veryactive accelerators.

As many apparently widely difierent embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that this invention is not limited to the specificembodiments thereof except as defined in the appended claims.

What is claimed is:

l. A vulcanizable polychloroprene composition having incorporatedtherein from 0.2 to 5.0% by weight of a bisthioamide selected from thegroup consisting of bisthioamides having the following formulae:

(a) N,N'-dibutyl-dithioadipamide (b) N,N'-dilauryl-dithio-adipamidewherein R is a monovalent hydrocarbon radical of from 1 to 20 carbonatoms, R" is a divalent hydrocarbon radical of from 1 to 20 carbon atomswith both valences on the same carbon atom and R is a divalenthydrocarbon radical of from 2 to 20 carbon atoms with the valences ondifierent carbon atoms.

2. A vulcanizable polychloroprene composition having incorporatedtherein from 0.2 to 2.0% by weight of N,N'-dibutyLdithioadipamide.

3. A vulcanizable polychloroprene composition having incorporatedtherein from 0.5 to 2.0% by weight of N,N'-dilauryl-dithio-adipamide.

4. A vulcanizable polychloroprene composition having incorporatedtherein from 0.5 to 2.0% by weight of N,N'-ethylene bis(thi0benzamide)5. A vulcanizable polychloroprene composition having incorporatedtherein from 0.5 to 2.0% by weight of 3,6-diisobutyl-2,S-piperazinedithione.

6. In the process of vulcanizing polychloroprene, the improvement ofincorporating before vulcanization from 0.2 to 5.0% by weight of abisthioamide selected from the group consisting of bisthioamides havingthe following formulae:

(a) N,N-dibutyl-dithio-adipamide (b) N,N'-dilauryl-dithio-adipamidewherein R is a monovalent hydrocarbon radical of from 1 to 20 carbonatoms, R" is a divalent hydrocarbon radical of from 1 to 20 carbon atomswith both valences on the same carbon atom and R' is a divalenthydrocarbon radical of from 2 to 20 carbon atoms with the valences ondifferent carbon atoms.

References Cited in the file of this patent UNITED STATES- PATENTSNaylor Nov. 15, 1955 UNITED STATES PATENT OFFICE CERTIFICATE OFCORRECTION Patent No. 2,852,498 September 16, 1958 Harris Walton Bradleyet alo It is hereby certified that error appears in the-printedspecification of the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 3, line 47, Table I third column thereof, for "60/200" read60/100 line 48, for "60/100" read 60/120 column 4, line '74, for "usedaddition" read we used in addition column 5, line 35, for "If" read Rline 39, for "0.2" read 0.5 a

Signed and sealed this 17th day of February 1959.,

SEAL) ttest:

KARL Ho AXLINE ROBERT C. WATSON Attesting Officer Commissioner ofPatents

1. A VULCANIZABLE POLYCHLOROPRENE COMPOSITION HAVING INCORPORATEDTHEREIN FROM 0.2 TO 5.0% BY WEIGHT OF A BISTHIOAMIDE SELECTED FROM THEGROUP CONSISTING OF BISTHIAMIDES HAVING THE FOLLOWING FORMULAE: